I would try advancing the timing then and see what happens. Couldnt hurt to try, just mark where it is now and if it doesnt make it better then put it back.
Here is a tip: Remove the dist cap. Put a rachet on the harmonic ballancer bolt and turn the motor back and forth. If there is lots of play in the timing set or dist gear then there will be a delay on the rotor turning.
I "THINK" I found the problem. The soft hose connecting the main fuel line from the gas tank has a major kink-flat spot in it. The line was recently replaced and looks like under vacuum pressure from the fuel pump it could easily flatten out. I'm going to replace the line and try out my theory. I'll keep you posted. Rock on, Shane :3gears:
Well here is the update: 1. New Fuel Pump 2. New Fuel Filter 3. New soft lines at pump, pump to carb, and at the gas tank 4. Full tune up: Set dwell, timing and carbs The car runs like a dream BUT it still has the stumble. I spent about half an hour today driving it to try and get more symptoms. SYMPTOMS: 1. Car REVS fine to 5K wth no stumble when not in gear. 2. In first gear at WOT the car starts to stumble hard at around 3500-4000RPM. The more I pay attention the more it seems as if the transmission is "slipping" or trying to shift early. 3. In third gear at 40 MPH when I floor it the transmission trys to shift down to first gear but it never engages. The motor revs to 3500RPM but it never finds first gear. When I let off the gas it goes back into third. 4. The "stumble" always happens around 3500RPM and only at WOT when the engine is under load. It does it in 1st gear from a stop and at WOT at speed when the passing gear tries to shift down into first. At this point I am starting to believe my problem is transmission related. Maybe it has something to do with the Vacuum Modulator but I am definately NO expert on tranny problems.
We still need to see fuel pressure at wide open throttle to rule out the fuel tank. Yes it's a pain to hook up a gage you can watch during a test drive, but it really is the very first thing I would have checked. My bet is the needle will be bouncing on zero just a moment before the bog occurs. If pressure is still as little as 2-3 psi, I agree you might want to start checking the trans. Devon
Do you know if you have a th350 or th400? If it has a square pan with one corner angled it s th400. The th400 has an electric kickdown while the th350 does not. If we know what trans you have we can help with that issue possibly. I assume the fluid level is okay? You may try to add a little bit more fluid and see if that solves the problem. Its not good to have too much fluid but if your trans is slipping its going to be toast soon.... Have you tried shifting the trans manualy with the column? If not try that and report back.
I had the same type of stumble...although my motor has alot more hp parts to it it turned out to be an over rich mixture. You may have with that new fuel pump have exposed a weak area in your carb and be causing an over rich condition....? Mark
Does anyone have a recommendation for the best way to run a fuel pressure gage to test the fuel pressure while I'm driving? I am not thrilled about the idea of plumbing fuel in to the interior to a dash mounted gage.
Take the hood off and plumb the gauge up where you can see it from the driver seat. Make sure you use fuel grade hose and do a burnout with the hood off for pictures!
You don't really have to take the hood off... just secure the gauge to the wiper and wind the fuel hose up there. Be careful of the connections and keep it away from heat sources!
UPDATE New coil installed. Still have a stumble. It is now doing it under partial load at any speed. It seems like possibly a carb problem. Maybe accelerator pump, float level, or dirty needles / seats?
UPDATE I installed a brand new Edelbrock 600 CFM 4 barrel and MSD Blaster 2 coil this weekend. (Both are identical to the old parts). Car still has the hesitation at part throttle and full throttle.
